1. Field of the Invention
The present invention relates to a magnetic head disposed at a trailing edge of a slider facing, for example, a magnetic recording medium, and in particular, to a method for manufacturing a magnetic head with a reduced thermal expansion due to a heat generation at a coil in the recording head.
2. Description of the Related Art
FIG. 14 is a partial longitudinal section illustrating a structure of a known magnetic head described in Japanese Unexamined Patent Application Publication No. 2001-52309. The thin-film magnetic head shown in FIG. 14 is an inductive head for recording.
According to the magnetic head shown in FIG. 14, (i.e., in particular shown in FIG. 2 in the patent document) a track width control portion 11 having a track width Tw is formed on a bottom core layer 10 composed of a soft magnetic material, such as Ni—Fe alloy. The track width control portion 11 has a layered structure including three layers, i.e., a bottom pole layer 12, a gap layer 13, and a top pole layer 14.
The length L1 of the track width control portion 11 is defined as a gap depth Gd of the magnetic head. The gap depth Gd is determined in advance to be a predetermined length, because the gap depth Gd greatly influences the electrical characteristics of the thin-film magnetic head.
A first coil layer 15 is formed at the back of the track width control portion 11 in a first direction (the height direction, i.e., the Y direction shown in FIG. 14). An insulating base layer 16 is formed between the bottom core layer 10 and the first coil layer 15 to insulate between both of the layers. The insulating base layer 16 is composed of, for example, Al2O3.
The first coil layer 15 is formed in a spiral pattern on the insulating base layer 16 with the first coil center 15a as the center. The first coil layer 15 is covered with a first insulating layer 17 composed of Al2O3.
A second coil layer 18 is formed in a spiral pattern on the first coil layer 15 with the first insulating layer 17 provided therebetween. The second coil center 18a of the second coil layer 18 is electrically connected to the first coil center 15a of the first coil layer 15.
The second coil layer 18 is covered with a second insulating layer 19 composed of an organic material such as a resist or polyimide. A top core layer 20 is patterned on the second insulating layer 19.
The top core layer 20 is formed such that the front end 20a is in contact with the track width control portion 11. The base end 20b of the top core layer 20 is magnetically connected to a lifting layer 21, which is composed of a magnetic material and is formed on the bottom core layer 10.
The bottom core layer 10, the bottom pole layer 12, the top pole layer 14, and the top core layer 20 are composed of a soft magnetic material, such as Ni—Fe alloy. The gap layer 13 is composed of a nonmagnetic material such as Ni—P alloy. The coil layers are composed of a conductive nonmagnetic material such as Cu.
In the inductive head according to FIG. 14, when a recording current is supplied to the first coil layer 15 and the second coil layer 18, a recording magnetic field is induced in the bottom core layer 10 and the top core layer 20. A leakage magnetic field is generated between the bottom pole layer 12 and the top pole layer 14, which are opposed to each other with the gap layer 13 provided therebetween in the track width control portion 11. A magnetic signal is recorded on a recording medium, for example, a hard disk by the leakage magnetic field.
In the inductive head shown in FIG. 14, the coil has the two-layered structure. Accordingly, the width T3 of the first coil layer 15 is decreased, thereby shortening the magnetic path formed from the bottom core layer 10 to the top core layer 20, thus decreasing inductance of the magnetic head and manufacturing a magnetic head adaptable to higher recording frequency.
According to a magnetic head disclosed in Japanese Unexamined Patent Application Publication No. 6-103526 (in particular disclosed in page 3 and FIG. 1 in the patent document), in order to decrease the coil resistance, coil layers at the rear end of the head have a thickness larger than the thickness of the coil layer at the top of the head covered with a top core layer and a bottom core layer. The coil resistance is decreased in this magnetic head, thereby suppressing the generation of thermal noise.
In a magnetic recording apparatus mounting a hard magnetic disk, the magnetic head described in the above patent documents is disposed on a slider, which floats over the magnetic disk with a minute distance.
According to the inductive magnetic head, the track width control portion 11 is expanded by the heat generation at the first coil layer 15 and protrudes from an air bearing surface (ABS), i.e., a face of the slider facing the recording medium.
Since a recording current applied to the first coil layer 15 has a high frequency, in particular, in a thin-film magnetic head for high recording density, the heat generation at the coil layer increases. The increase of the heat generation at the first coil layer 15 increases the thermal expansion of the track width control portion 11 and increases the amount of protrusion.
Furthermore, in a magnetic recording apparatus for high-density recording and high-speed recording, the gap between the recording medium and the slider is small. Accordingly, the protruded track width control portion 11 is frequently in contact with the magnetic recording medium, thus damaging the recording medium or the recording head itself.
In order to reduce the heat generation at the first coil layer 15, the first coil layer 15 must have a large cross-sectional area to reduce the resistance of the first coil layer 15. In particular, the resistance at the front portion of the first coil layer 15, i.e., the portion close to the track width control portion 11 rather than the lifting layer 21 must be reduced.
As described above, in order to reduce the inductance of the magnetic head by shortening the magnetic path formed from the bottom core layer 10 to the top core layer 20, the width T3 of the first coil layer 15 must be reduced. Accordingly, a width W1 of the first coil layer 15 (i.e., a width W1 in the Y direction shown in FIG. 14) cannot be increased.
A top face 11a of the track width control portion 11 must be flattened in order to ensure the junction between the top core layer 20 and the track width control portion 11. However, the magnetic head is too minute to flatten the top face 11a of the track width control portion 11 only. Accordingly, a top face of the 17a of the first insulating layer 17 becomes also flat. Since the first coil layer 15 must be covered with the first insulating layer 17, the top face of the first coil layer 15 cannot disposed above the top face of the 17a of the first insulating layer 17. That is, unlike the magnetic head described in Japanese Unexamined Patent Application Publication No. 6-103526, a plurality of coil layers cannot be simply stacked.